The present invention relates to a method of feeding strip paper on a dual-rod cigarette manufacturing machine.
On dual-rod cigarette manufacturing machines, cigarettes are usually produced by cutting crosswise and simultaneously two continuous cigarette rods formed by feeding respective paper strips through a filling station where a continuous layer of shredded tobacco is fed onto each strip.
Each strip and respective layer of tobacco is then fed through a forming fixture along which the opposite side edges of the strip are gradually folded together about the tobacco layer and then glued together to form a continuous cigarette rod, which, together with the other rod, is then cut into lengths by a single rotary cutting fixture operating at adjustable constant speed.
The said strips are usually fed through the machine by means of a feed device comprising a reel-off assembly for feeding a paper strip, twice as wide as the aforementioned strips, off a reel. The speed at which the said strip is reeled off is timed to the operating speed of the said cutting fixture in such a manner as to produce cigarettes at least theoretically of a given length.
The said feeding device also comprises a cutting unit for cutting the said strip longitudinally into the said two strips, each of which is usually run onto a respective conveyor extending along the said forming fixture and designed to feed the said strip along the same. Each strip and respective conveyor only mate in the presence of the said layer of tobacco which, when fed onto the said paper strip, provides for mechanically mating, by friction, the conveyor and respective paper strip. The friction coefficient between the conveyor and paper strip depends on a number of factors, such as the thickness, consistency and humidity of the tobacco layer, the humidity, elasticity and porosity of the strip, etc. Consequently, differing fluctuation in the respective said friction coefficients of the said two strips results in two problems: firstly, the length of the cigarettes coming off the machine is not always the same for both continuous cigarette rods; and secondly, only by chance does the actual cigarette length correspond with the theoretical length set by adjusting the speed of the reel-off assembly in relation to the operating speed of the cutting fixture.
On know types of dual-rod cigarette manufacturing machines, attempts have been made to solve both the aforementioned problems simultaneously by continuously controlling the operating speeds of the said conveyors in such a manner that, for each operation of the said cutting fixture, the length of the cigarettes produced is both the same for both rods and equal to a given reference length. As on-line detection of the respective lengths of the cigarettes produced from both rods poses serious difficulties, a proposal has been made to control the respective speeds of the said two conveyors as a function of a more readily detectable parameter varying in direct proportion to the length of the cigarettes produced.
Tests have shown, however, that, whenever the actual length of the cigarettes coming off the macine is greater or less than the set theoretical length, the tension of the respective paper strip between the respective conveyor and the said reel-off assembly is respectively greater or lower than the correct tension setting. One proposal already put forward for overcoming this drawback is to continuously detect the tension of each strip upstream from the respective conveyor and to employ signals, proportional to the difference between detected tension and a given reference tension value, for adjusting conveyor speed in such a manner as to eliminate the difference in tension and so produce cigarettes of the required set length.
Experiments conducted on the aforementioned system, however, can have revealed a number of serious drawbacks, mainly due to the tension of each strip fluctuating continually in relation to the given reference value. Such fluctuation, apparently caused by fluctuation in the friction coefficient between each strip and the respective conveyor, results in crosswise instability of the strips, each of which thus slips from side to side along the forming fixture and in relation to glueing devices on the said fixture for glueing together the opposite side edges of the strip. Instead of being straight, the respective bands along which the said pairs of opposite side edges are glued are therefore crooked and the resulting continuous cigarette rods of poor quality.